1. Field of the Invention
The present invention relates to a shelf unit which is a piece of equipment of a communication system, and particularly relates to a shelf unit in which modules accommodating dispersion compensating fibers are mounted.
Due to rapid increase of IP traffics, it is necessary to enhance transmission efficiency by increasing transmission capacity and/or making use of long-distance transmissions. A photonic network using a WDM (Wavelength Division Multiplexing) transmission system is becoming of an interest as a solution for achieving such enhanced transmission efficiency.
For a long-distance WDM network having a total transmission distance in a range of a several thousands of kilometers, regenerators are installed in the network at a certain interval. However, the distance between the regenerators is subjected to a limitation due to degradation of optical waveforms caused by wavelength dispersion in optical fibers. In order to suppress such wavelength dispersion, dispersion compensating relays may be provided in the network at a certain interval. With the distribution compensation relays being provided at a certain interval, the regenerators may be provided with an increased distance between them. Accordingly, total cost of the network can be reduced since less number of costly regenerators is required.
In an Ultra Long Haul WDM system aiming for a transmission distance over 3000 km without using regenerators, in order to achieve compensation with an increased efficiency, it is necessary to use DCF modules having dispersion compensating levels that correspond to the wavelengths of the signal.
FIG. 1 shows a dispersion compensating relay 10 provided with dispersion compensating fibers (DCFs) 11-1 to 11-n for optical paths xcex1 to xcexn, respectively. The dispersion compensating fibers 11-1 to 11-n are formed into modules to provide dispersion compensating fiber modules 12-1 to 12-n. The dispersion compensating fiber modules 12-1 to 12-n are mounted inside a shelf 13, which may be box-shaped. The dispersion compensating fiber modules 12-1 to 12-n are mounted in the shelf 13 to constitute a dispersion compensating fiber module shelf unit 14.
In FIG. 1, a receiving amplifier 15, a wave-dividing filter 16, a wave-combining filter 17 and a transmitting amplifier 18 are also shown.
The level of dispersion in an optical fiber depends on material and structure of the optical fiber and on the transmission distance. Also, various types of optical fibers are used among various communication common carriers and even if the same type of an optical fiber is used, the transmission distance may be different. Therefore, the dispersion compensation level of the DCF must be customized. Accordingly, there are various types of DCF modules for various dispersion compensation levels.
One of the parameters determining the dispersion compensation level is the length of the DCF. Particularly when compensating for a positive dispersion, a long DCF is required since the DCF has a small compensation level per unit length. Accordingly, the size of the DCF module increases with an increase of the dispersion level.
To build a system, various DCF modules are required for various transmission channels of the communication common carriers. Accordingly, there is a need for a mounting structure of a DCF shelf in which DCF modules with different width can be accommodated with improved efficiency.
2. Description of the Related Art
FIGS. 2, 3A and 3B are diagrams showing a dispersion compensating fiber module shelf unit 20 of the related art. The shelf unit 20 includes a shelf 21 provided with lower guide rails 22 and upper guide rails 23. Dispersion fiber modules 30, 40, 50 of different sizes are supported by the guide rails 22 and 23.
The shelf 21 includes a shelf main body 24, the guide rails 22, 23 and screw-hole plates 25, 26.
The shelf main body 24 is a rectangular box having an opening 22 at its front face and has a certain width W1 conforming to a global standard and has a certain size. The lower guide rails 22 and the upper guide rails 23 are fixed to the shelf main body 24 and are arranged at pitch P1. Screw holes 28 of the lower screw hole plate 25 and screw holes 29 of the upper screw hole plate 26 are arranged at pitch P2.
A dispersion compensating fiber module 30 of a first size has a width A which equals to the pitch P1 and accommodates a dispersion compensating fiber 31 of a predetermined length L1 wound on a reel 32. The module 30 is provided with a rail 33 on its upper surface, a rail 34 on its lower surface, a flange 35 on an upper end of the front side, a flange 36 on a lower end of the front side and an optical connector 37 on a central step part on the front side. The flanges 35 and 36 are provided with retaining screws 38 and 39, respectively.
A dispersion compensating fiber module 40 of a second size has a width 2A which is double the width A of the dispersion compensating fiber module 30 and accommodates a dispersion compensating fiber 41 of a predetermined length L2 wound on a reel 42. The length L2 is greater than the length L1. In a manner similar to the module 30, the module 40 is provided with rails 43, 44, flanges 45, 46 and an optical connector 47. The flanges 45 and 46 are provided with retaining screws 48 and 49, respectively.
A dispersion compensating fiber module 50 of a third size has a width 3A which is three-times greater than the width A of the dispersion compensating fiber module 30 and accommodates a dispersion compensating fiber 51 of a predetermined length L3 wound on a reel 52. The length L3 is greater than the length L2. In a manner similar to the modules 30 and 40, the module 50 is provided with rails 53, 54, flanges 55, 56 and an optical connector 57. The flanges 55 and 56 are provided with retaining screws 58 and 59, respectively.
A dispersion compensating fiber module 60 of a fourth size has a width 4A which is four-times greater than the width A of the dispersion compensating fiber module 30 and accommodates a dispersion compensating fiber 61 of a predetermined length L4 wound on a reel 62. The length L4 is greater than the length L3. In a manner similar to the modules 30, 40 and 50, the module 60 is provided with rails 63, 64, flanges 65, 66 and an optical connector 67. The flanges 65 and 66 are provided with retaining screws 68 and 69, respectively.
The dispersion compensating fiber modules are configured to have widths which are integral multiples of the width of the dispersion compensating fiber module 30 of a first size.
The dispersion compensating fiber modules 30, 40, 50, 60 are inserted into the shelf main body 24 in Y1-direction with the rails 34, 44, 54, 64 being engaged with and guided by the guide rails 22 and the rails 33, 43, 53, 63 being engaged with and guided by the guide rails 23. As shown FIG. 3A, the dispersion compensating fiber modules 30, 40, 50, 60 are mounted to the shelf main body 24 in such a manner that with the rails 34, 33, 54, 64 engaging the guide rails 22 and the rails 33, 43, 53, 63 engaging the guide rails 23, the flanges 35, 45, 55, 65 are fixed to the screw-hole plate 26 by screwing the retaining screws 38, 48, 58, 68 into the screw holes 29 of the screw-hole plate 26 and the flanges 36, 46, 56, 66 are fixed to the screw-hole plate 25 by screwing the retaining screws 38, 48, 58, 68 into the screw holes 28 of the screw-hole plate 25 so as to prevent the dispersion compensating fiber modules 30, 40, 50, 60 from sliding out of the shelf main body 24. The shelf unit 20 is in a state where the dispersion compensating fiber modules 30, 40, 50, 60 are closely mounted in the shelf main body 24.
It is to be noted that the dispersion compensation level depends on the signal wavelength. Accordingly, the length of the dispersion compensation fiber is proportional to the dispersion compensation level. Therefore, in some of the dispersion compensating fiber modules, particularly, the dispersion compensating fiber modules 40 of the second size, the dispersion compensating fiber modules 50 of the third size and the dispersion compensating fiber modules 60 of the fourth size 60, the dispersion compensating fibers 41, 51, 61 may not be fully wound on the reels 42, 52, 62. For such dispersion compensating fiber modules, there are unused spaces inside the modules. Therefore, the widths of such dispersion compensating fiber modules can be reduced to provide compact dispersion compensating fiber modules. Examples for such dispersion compensating fiber modules are a dispersion compensating fiber module 70 having a width which is 1.5 times greater than the width A and in which the dispersion compensating fiber is fully wound on the reel, a dispersion compensating fiber module 80 having a width which is 2.5 times greater than the width A and in which the dispersion compensating fiber is fully wound on the reel and a dispersion compensating fiber module 90 having a width which is 3.5 times greater than the width A and in which the dispersion compensating fiber is fully wound on the reel.
FIG. 3B shows a state where the above-described dispersion compensating fiber modules 30, 40, 50, 60 and the newly prepared dispersion compensating fiber modules 70, 80, 90 are mounted together in the shelf main body 24. The number of dispersion compensating fiber modules mounted in the shelf main body 24 is the same as the state shown in FIG. 3A.
It is to be noted that gaps 100 are formed adjacent the dispersion compensating fiber modules 70, 80, 90 having width that are not integral multiples of the width A. Therefore, the dispersion compensating fiber modules are not efficiently mounted in the shelf main body 21. What causes the gaps 100 is the fact that the guide rails 22, 23 are fixed to the shelf main body 21.
Accordingly, it is a general object of the present invention to provide a shelf unit which can obviate the problem described above.
It is another and more specific object of the present invention to provide a shelf unit which can improve the mounting efficiency by providing a shelf structure for accommodating dispersion compensating fiber modules having width that are not integral multiples of a predetermined width.
In order to achieve the above-object, a shelf unit includes:
a shelf having a box-like shape with an open front face; and
a plurality of modules having guide rails, the guide rail being engageable with a guide rail of a neighboring module.
The module is inserted into the shelf through the open front face such that the guide rail slide along the guide rail of the neighboring module. The module is connected to the neighboring module with the guide rail being engaged with the guide rail of the neighboring guide rail.
With such a shelf structure, the modules of any width can be mounted without gaps being formed between neighboring modules. That is to say, the modules can be mounted in a free-pitched manner without gaps between them. Accordingly, increased number of modules can be mounted in the shelf in comparison to the shelf unit of the related art.
Also, the width of the module need not necessarily be an integral multiple of a standard width. In other words, the module may be of any width. Therefore, modules without any unused space can be provided.